includes: add windows lean and mean guard.

When we drop gl.h some files pick up windows.h from here
without lean/mean and it causes conflicts.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14605>

include/c11/threads_win32.h

@@ -54,7 +54,9 @@ Configuration macro:
 #endif
 #define EMULATED_THREADS_TSS_DTOR_SLOTNUM 64  // see TLS_MINIMUM_AVAILABLE
 
-
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
 #include <windows.h>
 
 // check configuration

src/util/memstream.h

@@ -31,6 +31,9 @@
 #include <stdbool.h>
 #include <stdio.h>
 #ifdef _WIN32
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
 #include <windows.h>
 #endif